1. Field of the Invention
The present invention relates to a thyristor which may be controlled by light and having a semiconductor body which comprises at least four zones of alternating conductivity types, of which the first zone forms a main emitter, and the second zone forms a base, having a region provided to be exposed to light and having an auxiliary emitter located between this region and the main emitter.
2. Description of the Prior Art
A thyristor of the type generally set forth above is known in the art. In this thyristor, the auxiliary thyristor which consists of an auxiliary emitter and the other zones is turned on by light and the load current of the auxiliary thyristor is then employed to turn-on the main thyristor in the same way as in thyristors which are turned on by a control current. In order to prevent a violent heating on the thyristor at turn-on, it is desirable to ignite the auxiliary thyristor from the very start over as large a surface as possible. For this purpose, the light must strike the thyristor at a high intensity and in an extremely homogenously distributed fashion. This imposes strict requirements on the quality of the light source, but nevertheless does not always lead to the desired result, since inhomogeneous conditions in the thyristor itself also influence the turn-on process. In this case, and in the event of inhomogeneous illumination, the auxiliary thyristor will only ingite over a small area, and initially the entire load current will flow through this small area causing overloading of the thyristor and possibly destruction thereof.